Spark plug



J. A. DORAN Nov. l0, 1942.

SPARK PLUG 2 Sheets-Sheet 1 Filed Feb. 8, 1940 INVENTOR {Jigzis H. 170mm ATTORNEY J. A. DORAN Nov. 10, 1942.

SPARK PLUG Filed Feb. 8, 1940 2 Sheets-Sheet 2 ya 91 .w

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Patented Nov. 10, 1942 UNITED sTATEs PATENTy OFFICE SPARK PLUG James A. Doran, Providence, B. I. Application February 8, 1940, Serial No. 317,795

(ci. 12s-169) Claims.

This invention relatesA to improvements in spark plugs and has for an object the provision of a spark plug including a ceramic insulator at least a portion of which forms a solid barrier between the interior of the engine cylinder in which it operates and the outside atmosphere, said barrier having baked in, at the time the ceramic was made, a conductor formed of platinum or other metal oxidizable at an extremely low rate at the temperatures encountered in the ceramic ovens, thereby providing zero leakage therethrough.

Another object of the invention is the provision of a spark plug including a ceramic with a terminal well formed therein and a heat barrier between said well and the firing points to permit a lower temperature to be maintained in the terminal well than in the devices of the prior art.

A further object of the invention is the provision in a spark plug, of a ceramic insulator having a metallic annulus the interior of which is fused into the body of the insulator and the exterior of which forms a positive metal to metal seal with the shell.

Other objects and advantages of the invention will be apparent to those skilled in the art as the following specification is read on the accompanying drawings.

All types of spark plugs have heretofore been subject to considerable gas leakage between .the members, thus causing many serious results including overheating of the plugs, loss of compression and waste of fuel. Such leakage has been inherently difficult to overcome because the insulators must be sealed with metal electrodes interiorly and with metal shells exteriorly; and joining such totally opposite kinds of materials presents serious difficulties.

Furthermore, wide heat ranges must be endured which injuriously affect the sealing of the parts, due to the fact that the expansion of the metal members is so much greater than the expansion of the insulating member.

There are two sources of gas leakage through spark plugs:

(1) Between the center electrode and the insulator and (2) Between the insulator and the shell.

According to this invention the first source is foiled by eliminating a continuous bore through the insulator. The bore is broken by a solid wall of insulating material having a small platinum conductor extending therethrough and baked in when the insulator is made.

a thin metallic annulus built into the insulator at the time the insulator is made. This annulus projects outwardly from the insulator and permits a new method of sealing to be effected by the use of metal parts only. In other words, by having metal parts of the shell positively engage both sides of the annulus, zero leakage between the shell and insulator is very easily obtained.

Many attempts have heretofore been made to bake in electrodes or conductors into the porcelain or other ceramic used as an insulator but such attempts have failed because the electrodes or conductors would oxidize and a sealing bond between the metal and the porcelain could not be obtained. Many patents of the prior art casually state that the electrode is embedded in the porcelain at the time the insulator is made, but obviously the patentees did not actually try to do so, as they would have found out that it was impossible to obtain a gas tight seal due to the fact that the metal of which the electrodes is formed would have wasted away by oxidation at The second source is eliminated by means of the temperature at which the porcelain is baked. Another elect oi the kiln temperatures upon the electrodes is that they would be annealed and would also warp.

Referring to the drawings:

Figure l is an elevation in section showing one embodiment of the invention;

Figure 2 is a view of the ground electrode end of the plug in Figure l;

Figure 3 is an enlarged sectional view of the ceramic pellet positioned in the bore of the insulator of Figure l;

Figure 4 is a sectional elevation of a shielded type of spark plug embodying my new and improved double seal insulator;

Figure 5 is a perspective View of the upper portion of the insulator of Figure 4;

Figure 6 is the perspective view of the lower portion of the insulator, Figure 4; A

Figure '1 is a view of a metallic annulus adapted to be assembled in partly embedded relation with the upper and lower portion of an insulator;

Figure 8 is a view of a portion of a modified form of the annulus;

Figure 9 shows a further modification of the annulus of Figure '1;

` Figure 10 is a sectional elevation of an unshielded spark plug embodying further modifications of my sealing method;

Figure ll is a perspective view of the resistance unit shown in the plug in Figure 1;

Figure 12 is an enlarged sectional view of the compressible contacting disk, and Figure 13 is an enlarged cross-sectional view of the electrode shown in Figure 1;

Figures 14, 15, and 16 are sectional views of modifications of the electrode tip shown in Figure l;

Figure 17 is a lower plan view of the modification shown in Figure 14; and

Figure 18 is a cross-sectional elevation of a further modification of the plugs shown in Figures l, 4, and 10, one of the important features being the use of a two part insulator.

In all of the embodiments herein shown and described, the insulators are preferably made of ceramic materials, however any other suitable materials may be used. In using such other materials, the method of building up the insulators may vary due to the different temperatures encountered. However, the low oxidizing metal which I employ will stand the temperatures encountered and a sealing bond will be formed between the metal and the insulating material.

Platinum is especially satisfactory for this purpose, although any other suitable metal, or platinum alloys may be used, provided they have a sufficiently high melting point to withstand the heat of fusing and molding, and provided they are sufficiently non-oxidizable to withstand the oxidizing effects of the insulating materials employed. It is furthermore highly important that such a metal should have as nearly the same coeiliicent of expansion as the insulating materials as possible, to insure against leakage at various temperatures.

Referring first to Figure l, the metal shell 20 has mounted therein an insulator 2|, having a bore 22 extending therein from the electrode end, and a barrier or dam 24 is formed therebetween.

Through this barrier or dam 24 is a metallic Wire 25 preferably of a low oxidizable material, for example platinum which is bonded to the ceramic or other material of which the insulator is made, so that gases from the cylinder cannot leak through.

One reason why the Wire 25 is preferably small in diameter is that, in using precious metals, the cost per unit is very low; and another reason is that the heat conduction of the wire is very low, thereby maintaining the terminal end of the plug at a much lower temperature than in plugs of the prior art. This is particularly valuable in plugs of the well type such as illustrated in Figure 4.

In making insulators of ceramic materials it is sometimes convenient to extrude the ceramic from presses in continuous tubular form with a small hole through the center. This hole may be approximately the diameter of the electrode. Lengths of the tubular extruded material are cut off, then placed on the mandrels and the outside is turned to the size and shape required. If the hole through the center needs to be of some special shape or form, for example threaded, etc., this is done after the mandrel is removed. However, the hole extends all the way through; so in order to provide a barrier or dam such as 24, a separate pellet 24a such as is shown in Figure 3 is made with a hole extending longitudinally through the center and a length of small platinum wire 25a is placed in the center hole of the pellet. In order to retain the wire in place, it may have a knot formed therein as shown in Figure 3.

The pellet 24a is then pushed into the central hole of the insulator such as 2| until it rests tion shown in dotted lines in Figure l. A -ilux or glazing material is placed between the joints and bearing surfaces in order to insure that the fusing operation will bond the insulator, the pellet and the platinum together. After being vitried, the upper end 26 of the wire 25 is bent down, and the lower end 21 is bent up as shown, and the insulator assembly is complete.

The electrode 23 is then screwed into the threaded hole 23 with a soft metallic disk 29 contacting against the bent end 21 oi' the wire 25, thereby establishing contact between the electrode 28 and the wire 25. Due to the fact that the disk 29 is soft and compressible it also absorbs mechanical variations and permits the electrode head 30 to firmly enclose the insulator tip 3|.

On the electrode 23 are flat spots 32 embedded in cement to prevent it from loosening. On the lower portion of the electrode stem is a metal tube 33 of the same external diameter as the screw thread 34. This tube is preferably made of copper in order to accelerate heat transmission from the nring head 30. The tube is placed on the stem of the electrode before the thread 34 is rolled. Figure 13 illustrates this construction in which the head 30 is upset on the end of the stem, the stem then being of the smaller diameter its entire length. The snugly fitting copper tube is then placed upon the stem abutting upon the upper portion. 'lhe stem is then rollthreaded, which operation enlarges the diameter of the stem, and holds the tube in firm engagement between the head 30 and the thread 34.

This electrode construction, wherein a. tube is utilized to obtain an increase of diameter equal to the diameter of a rolled screw thread, is highly valuable and novel method applicable to many arts and uses where a rolled thread is desirable, and where at the same time a full diameter stem is necessary.

The terminal screw 35 is set down firmly against a resistance unit 36 contacting a compressible cupped disk 31 which in turn makes a positive contact with ythe turned over end 26 of the wire 25. A terminal flange 38 is mounted on the screw 35 snugly against the insulator, while 39 is a conventional terminal nut.

.After assembling the insulator 2| in the shell 2U, a gasket 40 is rst placed in position in the shell, followed by the insulator assembly. A metal tube 4| forces the insulator against the gasket 40, and seals the insulator in the shell; such pressure being exerted when the electrode 42 is pressed against the sleeve 4| by the pressure from the curling or spinning over of the lower edge 43 of the shell.

Before assembling the metal parts in the insulator, all surfaces are coated with a suitable sealing cement or compound to insure the thermal conductivity between the members and to prevent the loosening of electrode 28 and terminal screw 35. Likewise, before assembling the insulator in Ithe shell, all bearing surfaces are preferably coated with a compound that will maintain the maximum thermal conductivity between all the interior members and the shell. The tubes 33 and 4| are coated with compound for the purpose of rapidly extracting heat from the ground electrode 42 and from the electrode head 30, and rapidly transmitting such heat to against the shoulder therein, assuming the posithe radiating flanges of the shell.

IThe shielded type Plug shown in Figure 4 shows a modification of the arrangement shown in Figure 1, in which in addition to providing a solid barrier to gases tending to pass through 68 of the shell. The gasket '6.3 acts as a thrust the insulator, a second solid barrier is provided washer to support the insulator against cylinder through which it is impossible for any gases to pressures, and thus relieves the flange 50 from leak through between the insulator and the shell. bearing such mechanical stresses. The flange 50 The shell 45 i's preferably provided with a 5 being severely compressed between the shoulder maximum number of thin radiating flanges 46, 65 and the sleeve y66 functions as n sealing meminasmuch as this type of plug is commonly used ber to prevent gas leakage betwem the insulator on aircraft engines operating under very high and the shell. temperatures. The insulator is composed of an The carbon resistance member 60 should be upper tubular portion 41 and a lower portion 48. 10 of about fifteen hundred ohms resistance in or- In the lower portion 4-8 is a pellet 2i24, in which der to serve as a means for overcoming the cais located conducting wire 225 with bent-over pacitance existing between the metal conduit ends 226 and 221. and the conducting ignition cable in a shielded In constructing the insulator a thin platinum ignition system, however other values may be disk is provided, such as that shown in Figure 7 15 employed in accordance with the conditions unand designated by the numeral :50, or it may be der which the plug is to be used. Thus. the reof the modified forms |50 shown in Figure 8. sistor 60 also serves to reduce the burning away or 250 shown in Figure 9. The upper part 41 A of the electrodes 39 and 42; -it being particularly is made tubular as shown in Figure 5, and the efficient because of its location so close to the lower part 48 Figure 6 has a reduced portion 20 electrodes. In engines where the heat is not 49 thereby forming a shoulder 5| upon which excessive, this resistor could be located between the platinum washer 50 may rest. The reduced the conductor wire |25 and the electrode stem portion fits the hole in the washer 50 and also 55. fits the interior hole formed in the tubular por- The metal sleeve 66 may be of any material tion 41. 2 desired but I prefer to use copper due to its high The portion 48 of the insulator has a bore 53, yconductivity for conducting heat from the ground bounded by the pellet 224, after the latter is electrode '61 and also from the insulator to the placed in the bottom of the bore 54, portions of shell. In the plug of Figure 4, cement or comthe bores 53 and 54 are threaded to accommopound is applied to the insulator and the sleeve date matching ythreads on the electrode stem to form bonds therebetween to facilitate the disand the terminal shank respectively. The ceramic sipation of heat. parts having Ibeen formed up and having been The carbon resistance member 36 in Figures coated with suitable flux or the like are assem- 1 and 2 is used as a radio suppressor and for such bled as follows: The pellet 224 having a knotted purpose should be of about twenty thousand ohms platinum wire 225 therein is pushed in the shoulresistance. Suppressors are ordinarily mounted dered end 49 until it reaches the bottom of the exterior to the plug itself; but the suppressing bore 54. The platinum washer 50 is slipped over action is more efficient when the resistor is lothe boss 49 and caused to rest on shoulder 5|, cated as close as possible to the sparking gap. after which the sleeve 41 is slipped on the boss An unshielded spark plug wherein the insulaand pushed down until it touches the upper face tor is mounted from the top of the shell '80 of the washer 50, leaving the projecting part is a further modification shown in Figure 10. of the washer to form a projecting flange. The In this figure a modified form of fused-in wire assembly is then placed in a furnace or kiln to is shown instead of the pellet arrangement above vitrify the ceramic and seal in the conducting described. This insulator is made of two porwire 225 and the projecting flange 50. 'Due to 45 tions; an upper portion 10 and a lower portion the fact that the coeiicients of expansion of the 1| with a metal collar 12 fused between the two platinum and the ceramic are nearly equal, and portions. The conducting wire 13 is mounted due to the fact that the platinum can stand the in the lower portion 1|, and carries a firing tip heats encountered for the required amount of 14 which is embedded within and has its face time the surfaces of the platinum form a bond ilush with the tip of the insulator. The electrode or permanent seal with the ceramic, which bond 14 and the wire 13 must both be of a substanis not affected by any conditions, no matter how tiallynon-oxidizable metal inasmuch as it is extreme, under which the insulator, or the plug placed in position, together with the wire 13 and in which it is embodied, may have to work. the collar 12 before the portions are fused to- The electrode 55 has a head 56 enclosing and 55 gether and vitriiled. reinforcing the tip of the insulator. The elec- -After being vitriiled, the terminal screw 1'5 trode 55 is screw threaded at its upper end, and is screwed ilrmly down against the disk 16 in presses firmly against the compressible disk 51, order to contact with the bent portion of the conto insure positive contact against the end 22.1 ducting wire 13. The complete assembly is then of the conducting Wire 225. The electrode also placed in the shell 80 with the flange 12 resthas a copper tube 58 to accelerate heat dissipaing on the shoulder 11, while a sleeve 18 is intion from the head 56, and flattened portion 59 serted from the top of the shell to contact 12. for cement facilitates the locking in of the elec- The curling over oi.' the upper edge 19 creates trode. In the upper portion of the insulator pressure upon the insulator body and upon the is a carbon resistance 60 contacting against vthe G5 iiange 12 to effect a metal to metal gas-tight seal end 226 of the conducting wire 225, under presbetween the insulator and the shell. All bearing sure from the terminal screw 6|. In the upper surfaces between terminal screw 15 and the inend of the screw 6| is a tapped hole 62 into which sulator, as well -as the bearing surfaces between any suitable connector device may be screwed. the insulator and the shell are preferably coated The entire insulator assembly is then placed with a cement compound before assembly for in the shell 45 with a gasket 63 resting against the purpose of obtaining a bond promoting maxian upper ledge 64 of the shell. The flange 50 mum thermal flow. A is secured against the shoulder '65 by the me- In this constructicm the ring tip 14 is further tallic sleeve 56, being held under positive presprotected against overheating by reason of it sure by the electrode '51 and the curled over edge 75 being embedded in the insulator tip and thus is protected against cylinder temperatures on all surfaces excepting its face. In this construction, platinum or a platinum alloy can be used as the firing electrode most advantageously, as it does not readily oxidize'and burn away; therefore, a comparatively thin disk may be used in order to keep the cost of the material down to a point that is not prohibitive. The ground electrode 8| is similar to the ground'electrode 42 except that its central portion is of a diameter to correspond with the electrode face '|4.

In Figures 14 and 17, the electrode 14a has tapered holes I8 and lugs I9 formed therein. Before the ceramic is fused, the electrode is coated with' flux or glazing material and applied to the ceramic. By fusing, the tapered holes |8 and the space around the lugs I9 are lled with glaze, and a portion a which covers the end of the electrode 'Mais ground oil to expose the face of the electrode.

Figure l shows another form of the electrode, wherein the conducting wire 13b passes through the electrode 82a so that the two members may be riveted or welded at 84. Figure 16 shows another form of electrode tip wherein a wire 85 is formed spirally, and fused or glazed to the insulator when the latter s being vitrifled.

In the modification shown in Figure 18, the shell 90 has a bore 9| extending in from one end thereof and a bore 92 extending therein from the other end, the portion 93 between said bores being of reduced diameter and forming a ledge. A thin annulus |0`| is provided on the firing chamber end, and a second annulus ||2 is provided on the terminal well end.

The insulator is comprised of two parts. The upper part 94 is a plain straight sleeve. It may be of ceramic material, glass, or any other suitable material. The lower part consists of a portion 95 over which a portion of the length of the sleeve 94 extends, a shoulder portion 96, a straight portion 91 and a tapered portion 98 at the bottom as shown in Figure 18. From the bottom a threaded hole extends upwardly along the center line to a point above the middle of the lower part. From the upper end a threaded hole extends downwardly.

Between the threaded hole ||3 and the threaded hole 99 extends a platinum wire |00 having its ends extending into said threaded holes.

When the lower part of the insulator is formed up, prior to vitrii'ying the same, a small hole is formed joining holes 99 and ||3, and a knotted or bent platinum wire is inserted. Suitable flux or the like is applied and the insulator member is placed in the kiln or oven to vitrify the same l with the result that the platinum wire is fused in and thereby an imperforate barrier is formed in the insulator between the threaded holes 99 and |I3. The protruding ends of the platinum wire are bent over. A washer |03 of soft material is forced into intimate contact with one end of the platinum wire when the screw |0I carrying the electrode |02 is screwed in, and since the washerl is soft the electrode may be brought right up to the lower end of th'e insulator. The screw |09 when screwed into the hole I I3 forces soft washer |08 into intimate contact with the upper end of the platinum wire |00. It is of course necessary to apply a cementitious compound to the screws before they are applied to the insulator and it is also under understood that the bearing surfaces of the upper and lower portions of the insulator are also coated with a sealing and bonding com- 2,so1,ese

pound before they are assembled into the shell.

The order of the assembly hereinafter described need not be followed literally, as any order capable of giving as a resultant, the arrangement shown in Figure 18 may be followed.

The lower portion of the insulator (having the electrode end screwed in and the terminal screw assembled therein), has a suitable sealing gasket |04 positioned on the upper surface of its shoulder 98 and, sufficient sealing compound having been applied to all of the bearing surfaces, the insulator is then inserted through the bottom of the shell until the gasket |04 encounters the ledge 93. after which a copper sleeve |05 also having had compound applied thereto is inserted into the shell from the bottom. Following this the ground electrode is applied and the annular rim |01 is spun over, thereby forcing the sleeve |05 against the shoulder 98 and th'e shoulder and the gasket |04 against the annular ledge 88, thereby effecting a seal between the ledge and the shoulder with the gasket therebetween.

The sleeve member 94, having been coated with compound is then inserted into the shell from the upper or outer end, whereby it overlaps the upper portion of the lower insulator member and comes to rest on the upper surface of the ledge 93. The gasket which may be of lead and serves as a cushioning member is then inserted and the thin annular rim ||2 is then spun down onto the gasket The distance from the terminal screw |09 along the top of the lower insulator member, and thence downwardly, between the sleeve 94 and the lower insulator member, to the ledge 93 is far greater than the greatest safety distance, therefore this plug with the two piece insulator has an ample factor of safety plus the following advantages:

1. The two part insulator permits the manufacture of 50% more units per day as the sleeve portion may be produced by extrusion and a cutting off operation, and the lower part of the insulator has fewer operations and can therefore be formed up more rapidly than any of the other forms herein described; therefore, the two part insulator shown in Figure 18 costs less to produce.

2. The length oi' platinum conductor may be applied to and fused into the lower insulator member directly instead of employing the pellet hereinbefore described.

3. The short length of insulator (shoulder) between the copper tube and the gasket tends to fully compensate for the unequal expansions of the steel of the shell, the copper tube and the ceramic of the insulator. In Figure 18 the proportions are for the ceramic 1.0 as against the copper tube 0.6, plus 0.4 for the steel.

4. A sealing and bonding compound is applied to all bearing surfaces to facilitate the dissipation and disposal of heat from the electrodes.

5. The platinum wire is small in diameter and in addition to forming an imperforate barrier against the leakage of gases therethrough, it also permits a heretofore unattained low rate of conduction of heat from the firing chamber, and the electrode, to the terminal well of the insulator.

In this application, I have shown the advantages of a conducting wire being fused into an insulator, and also a flange being fused into the exterior walls of an insulator:`b`oth features as adaptable and advantageous for spark plug practice. However, I wish it understood that I do not limit this invention to this particular use since it isadaptable to various electrical devices where the advantages of an interior conductor and an exterior supporting flange are of value.

Having described my invention, I claim:

1. In a spark plug, an insulator having an electrode circuit therethrough including a length oi precious metal fused into said insulator and forming an imperforate barrier between the firing chamber and the exterior of said plug, said metal having a coefficient of expansion similar to that of the insulator and being capable of standing the high temperatures of the kiln in which said insulator is fused, for the required length of time without oxidizing,

2. The method of making a ceramic insulator for spark plugs or the like which includes the step of forming said insulator of unfused material with a passage therethrough, the step of applying a length of non-odidizing conductive material in at least a portion of the length of said passage, and the step of fusing said insulator and said conductive material together to form a vitrified imperforate body.

3. The method of making insulators for spark plugs or the like which includes the step of forming an insulator body of ceramic material with a longitudinal passage therethrough, the step of forming a pellet of ceramic material having a small passage therethrough, the step of applying a length of nonoxidizing conductive material in said last mentioned passage, the further step of positioning said pellet within said rst passage. and the step of fusing the above named parts together to form an insulator having a barrier therein, imperforate to the passage of gases therethrough, yetfreely permitting current to pass therethrough.

4. The method of making insulators for spark plugs which consists in forming a body of unfused ceramic material, forming a hole therethrough at least a portion of the length of which is of minute diameter, inserting a conductor formed of nonoxidizing material in the portion of minute diameter, and fusing said body to vitrify the same and to bond said conductor therein.

5. In spark plug, an insulator body having a bore extending therein from the terminal end thereof, a second bore extending therein from the electrode end, a barrier in said body between said bores having a platinum conductor extending therethrough and bonded therewith to form a permanently impervious dam through which gases under pressure cannot pass.

6. A spark plug insulator formed of ceramic material, said insulator having a terminal bore extending therein from one end, an electrode bore extending therein from the other end thereof, an imperforate body of material between said bores, and a conductor fused into said body and extending from one of said bores to the other.

7. An insulator according to claim 6 in which a terminal member is mounted in said first mentioned bore inv contact with said conductor, and in which an electrode member is secured in said second mentioned bore in contact with said conductor, whereby current may readily pass through said insulator, but gas under pressure cannot.

8. The method of making a spark plug insulator which consists of forming a body of unfused ceramic material with a threaded hole extending therein from one end, a larger threaded hole extending therein from the other end, and an unthreaded hole therebetween, forming a pellet of unfused ceramic material, placing a non-oxidizing conductor in said pellet with its ends extending therefrom, mounting said pellet in said unthreaded hole with iiuxing material therebetween, and fusing said ceramic materials to form a unitary imperforate insulator.

9. The method of making a ceramic insulator for spark plugs which includes, the step of extruding the ceramic material from an unfused ceramic mixture under pressure to form a continuous tube of said material with a small concentric hole extending longitudinally therethrough, the further step of cutting the extruded material off in lengths, the step of externally shaping said lengths by turning, the step of positioning in the hole in each of said lengths an electrode conductor, and the step of fusing said lengths in a kiln or oven to produce fused insulators having said' conductors fused into and bondcd therewith to form an imperforate body.

10. The method of making an insulator for spark plugs or the like which consists of, forming a body of an unfused ceramic mixture, a longitudinal hole being formed therein simultaneously with the forming of said body, at least partially embedding an electrode in one end of said insulator, said electrode being formed of non-oxidizing metal and having a conductor connected thereto and extending into said longitudinal hole, and the step of vitrifying said body and bonding said electrode and said conductor together to form an imperforate body.

JAMES A. DORAN. 

